Polymers of carbon monoxide and olefins, such as ethylene, have been known and available in limited quantities for many years. For example, polyketones are disclosed in Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, Vol. 12, p. 132, 1967, and in Encyclopedia of Polymer Science and Technology, 1968, Vol. 9, 397-402. The low molecular weight copolymers in particular may be used as intermediates for the production of plastics, as components in blends with other polymers (such as waxes and greases) and as pour-point depressants for middle distillate petroleum fuel products. The higher molecular weight polymers have use and utility as premium thermoplastics for fibers, films, injection molding, compression molding or blowing applications.
High molecular weight linear polymers of carbon monoxide and ethylene in which monomer units occur in alternating order and which polymers consist of units of the formula ##STR1## can be prepared by using Group VIII metal organic phosphine compounds as a catalyst, such as palladium organic phosphine compounds. For example U.K. Pat. No. 1,081,304, U.S. Pat. No. 3,689,460, and U.S. Pat. No. 3,694,412 disclose processes using palladium catalysts having monodentate alkyl phosphine ligands. Similar palladium catalysts having monodentate phosphine ligands are disclosed in the articles found in J. Am. Chem. Soc. 1982, 104, 3520-2, Organometallics 1984, 3, 866-70, Proc. Ind. Assoc. Cult. Sci. 1985, 68B, 1-5 and CHEMTECH 1986, 1, 48-51. European Patent Application No. 121,965 discloses a process for polymerizing CO and an alkenically unsaturated hydrocarbon using a Group VIII metal complex having bidentate phosphorous, arsenic or antimony ligands. Application of these catalysts to a monomer mixture which, in addition to carbon monoxide and ethylene, comprises at least one olefinically unsaturated hydrocarbon having the general formula C.sub.x H.sub.y, which hydrocarbon has fewer than 20 carbon atoms and contains an olefinically unsaturated --CH.dbd.CH-- group, leads to the formation of polymers with units of the formula ##STR2## and units of the general formula ##STR3## occurring randomly distributed within the polymer. The structure of the copolymers and "terpolymers" differs only in that in the case of the "terpolymers" a unit of ##STR4## is encountered at some random places in the polymer instead of a unit of ##STR5##
The polymers have excellent mechanical properties; especially, very high strength, rigidity and impact resistance. Despite the fact that they can be prepared fairly simply from very cheap raw materials with the aid of a suitable catalyst, problems with processing these copolymers have limited their practical application up to now. This is mainly due to their high melting point of about 257.degree. C. and the consequent problems in processing them. The processing of these copolymers by, for example, injection molding, should be carried out in a molten state with the material being at a temperature of at least 25.degree. C. above its melting point, in this case at a temperature of above 280.degree. C. It has been found that these copolymers are not sufficiently resistant to such high temperatures; they discolour and decompose. Lower melting points and consequently improved processability in the melt can be obtained by incorporating a second unsaturated monomer in the molecular chains, for example propylene.
However, there is a second factor that has an unfavourable influence on the processability of the copolymers at the melt temperature. This is the fact that copolymers that can be obtained by the possible catalytic copolymerization processes will always contain a certain amount of impurities, such as catalyst residues, copolymer with a relatively low molecular weight, oligomers, water and solvent residues. The last of these will not, of course, be present if gas-phase copolymerization is employed, but will be present if suspension methods are used. The presence of these impurities means that when heating to melt temperature, the volatile impurities contained in the copolymer are released as gaseous products in amounts that are greater than can be tolerated in customary devolatilizing extruders. This quantity can be estimated at about 3%w.
There is therefore a need for a working-up method which can provide sufficient purification of the copolymers. More in particular, there is a need to provide copolymers of carbon monoxide, ethylene and optionally at least one olefinically unsaturated hydrocarbon that contain no more than 3%w of the impurities (a) water, (b) organic solvent and (c) by-products that escape in the gaseous state on heating to the melt temperature of the copolymer. Said upper limit is a total content of the impurities (a), (b) and (c) together.